The present invention relates to a spool valve system.
Various types of solenoid valves are installed in a hydraulic circuit of an automatic transmission that is mounted in a vehicle. Each solenoid valve includes a solenoid portion and a valve portion. The valve portion is driven by supplying electric current to a coil of the solenoid portion. The valve portion opens and closes oil passages, adjusts the oil flow volume, and adjusts the hydraulic pressure.
FIG. 1 is a sectional view of a conventional linear solenoid valve. In FIG. 1, reference numeral 11 denotes the solenoid portion, and reference numeral 12 denotes a pressure adjustment valve portion that serves as the valve portion and is operated by driving the solenoid portion 11. The solenoid portion 11 includes a coil assembly (not shown in FIG. 1), a plunger 14 that is installed such that it advances and retracts (moves to the left and right in FIG. 1) freely in relation to the coil assembly, and the like. A rear end (the right end in FIG. 1) of a spool 26 in the pressure adjustment valve portion 12 is brought into contact with a front end face S1 (the left end face in FIG. 1) of the plunger 14.
The plunger 14 is drawn by the coil in the coil assembly with a prescribed attractive force such that a thrust force is generated in the plunger 14. The thrust force is transmitted to the spool 26 such that the pressure adjustment valve portion 12 is operated, the flow volume of oil is adjusted, and the hydraulic pressure is adjusted.
The pressure adjustment valve portion 12 includes a sleeve-shaped valve main body 62, the spool 26, an end plate 64, a spring 44, and the like. The spool 26 is installed such that it advances and retracts freely, and slides freely in relation to the valve main body 62. The end plate 64 is fixed to the front end (the left end in FIG. 1) of the valve main body 62 by helical threads. The spring 44 is installed between the end plate 64 and the front end of the spool 26 and energizes the spool 26 toward the solenoid portion 11 under a prescribed spring load. Note that the valve main body 62 is attached to a valve body (not shown in FIG. 1) by a prescribed method, such as press-fitting for example.
The spool 26 includes a medium-diameter land 66, a groove 67, a large-diameter land 68, a small-diameter groove 69, a large-diameter land 70, and a small-diameter plunger contact portion 71. The land 66 is formed at the front end of the spool 26. The groove 67 is a small-diameter portion between lands 66, 68 that is formed adjacent to and rearward (rightward in FIG. 1) of the land 66. The land 68 is formed adjacent to and rearward of the groove 67. The groove 69 is formed adjacent to and rearward of the land 68. The land 70 is formed adjacent to and rearward of the groove 69. The plunger contact portion 71 is formed adjacent to and rearward of the land 70.
A concavity 75 is formed on the rear end face (the right end face in FIG. 1) of the end plate 64, and a concavity 76 is formed on the front end face of the land 66. The spring 44 is installed such that its front end is positioned in the concavity 75, and its rear end is positioned in the concavity 76. The end plate 64 not only prevents the spool 26 from protruding from the valve main body 62, but also serves to adjust the spring load. The spring load can be adjusted by rotating the end plate 64 such that it moves forward or rearward.
The valve main body 62 includes an input port p1, an output port p2, a feedback port p3, and a drain port p4. An input pressure is supplied via the input port p1. The output port p2 outputs an output pressure to a shift valve (not shown in FIG. 1). The drain port p4 discharges the input pressure. The feedback port p3 is connected to the output port p2 via a feedback oil passage (not shown in FIG. 1) that is formed outside the valve main body 62. The output pressure is supplied as a feedback pressure, generating a feedback force that corresponds to the difference in the surface areas of the lands 66 and 68 and that pushes the spool 26 rearward.
Therefore, the spool 26 receives the thrust force from the plunger 14, the spring load from the spring 44, and the feedback force from the feedback pressure, and with the plunger contact portion 71 in a state of contact with the front end face S1, the spool 26 advances and retracts as a single unit with the plunger 14.